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Nitrate & Nitrite

Recognized Treatment Techniques For Meeting Drinking Water Regulations For The Reduction Of Nitrate & Nitrite From Drinking Water Supplies Using Point-of-Use/Point-of-Entry Devices And Systems




Recognized treatment techniques for meeting drinking water regulations for the reduction of nitrate and nitrite using point-of-use and point-of-entry (POU/POE) devices and systems.


Most nitrogenous materials in natural waters tend to be converted to nitrate, so all sources of combined nitrogen, particularly organic nitrogen and ammonia, should be considered as potential nitrate sources. Primary sources of organic nitrates include human sewage and livestock manure, especially from feedlots. The primary inorganic nitrates which may contaminate drinking water are potassium nitrate and ammonium nitrate both of which are widely used as fertilizers. According to the Toxics Release Inventory, releases to water and land totaled over 112 million pounds from 1991 through 1993. The largest releases of inorganic nitrates occurred in Georgia and California. The principle sources of nitrate contamination in water are thus fertilizers, animal waste, and septic tank wastes. EPA has found nitrate in excess of 10 mg/L in over 800 small, rural groundwater systems. The water supplies most vulnerable to nitrate contamination are obviously in agricultural areas and in well waters having a close or hydraulic relationship to septic tanks. Only 10 percent of the wells surveyed in a recent U.S. EPA groundwater study, however, had nitrate levels above 20 mg/L. High nitrate is the most frequent reason for shutting down wells in the United States.

Health Effects

Nitrate in drinking water can be responsible for a temporary blood disorder in infants called methemoglobinemia (blue baby syndrome). In infants less than six months old, a condition exists in their digestive systems which allows for the chemical reduction of nitrate to nitrite. The nitrite absorbs through the stomach and reacts with hemoglobin to form methemoglobin, which does not have the oxygen carrying capacity of hemoglobin. Thus, the oxygen deficiency in the infant's blood results in the "blue baby" syndrome. When the nitrate-contaminating source is removed, the effects are reversible. Since ingestion of water containing high nitrate concentrations can be fatal to infants and livestock, the U.S. EPA has established a level of 10 milligrams peer liter (mg/L) total nitrate (measured as nitrogen) as the Maximum Contaminant Level Goal (MCLG) and Maximum Contaminant Level (MCL) in drinking water. This is equivalent to 44.2 mg/L when measured as nitrate ion. The Agency has also established an MCLG and an MCL of 1 mg/L for nitrite (measured as nitrogen) as well as the 10 mg/L MCL for total nitrate plus nitrite (measured as nitrogen). Although extreme levels of nitrate can be associated with central nervous disorders in adults, it should be noted that nitrates and nitrites are rarely a problem in drinking water for humans older than six months of age.


Treatment Alternatives

Current technology suggests that several techniques may be used for removing nitrate from drinking water including chemical reduction, ion exchange, reverse osmosis, electrodialysis, and distillation. At the present time, it appears that three methods, ion exchange, distillation, and reverse osmosis, are considered to be practical and economically feasible for nitrate removal when considering POU or POE devices. It must be recognized that devices that remove nitrates may have varying effectiveness based on the amount of nitrate in the water supply and the balance of other ions in the water. The ion exchange process, for example, is sensitive to waters containing high TDS, high sulfate, and high hardness levels (which can cause hardness precipitation during regeneration). Effective anion exchange removal of inorganic nitrate requires softening pretreatment ahead of the anion exchanger when hardness is present above 10 grains per gallon to prevent exchanger fouling. Care must be taken in the choice of anion resin to avoid "dumping" of nitrates--a condition where effluent nitrate levels can exceed influent levels due to selectivity of sulfates over nitrates. Nitrate dumping can result in effluent concentrations of nitrate equaling the equivalent sum of nitrates plus sulfates and other preferred anions in the incoming water supply. The use of nitrate "selective" resins can avoid this and is recommended in systems that are unmonitored or for POU cartridge applications. Brine reclaim should be avoided because excess nitrates in the recycled brine can lead to excessive nitrate leakage in the subsequent run. Anion resins are lower in density than softener resins and are backwashed at lower rates. Commercially available line pressure and pump driven reverse osmosis membranes systems reduce nitrates from water by 60 to 95 percent, even at nominal 50 pounds per square inch (psi) pressure and at 45° to 70° F. Cellulosic membranes should not be used for nitrate reduction in line pressure applications. Thin film composite (TFC) membranes are more effective for nitrate reduction especially in household line pressure applications where feed pressure to the RO membrane may fall below 60 psi. For effective reduction of nitrates with RO treatment using a line pressure unit, the RO feed pressure should be always maintained above 40 psi and maximum nitrate influent concentration should not exceed 30 mg/L measured as nitrogen. For back up on POU systems, nitrate selective ion exchange cartridges can be used as polishers. The treatment methods listed herein are generally recognized as techniques that can effectively reduce the listed contaminants sufficiently to meet or exceed the relevant MCL. However, this list does not reflect the fact that point-of-use/point-of-entry (POU/POE) devices and systems currently on the market may differ widely in their effectiveness in treating specific contaminants, and performance may vary from application to application. Therefore, selection of a particular device or system for health contaminant reduction should be made only after careful investigation of its' performance capabilities based on results from competent equipment validation testing for the specific contaminant to be reduced. As part of point-of-entry treatment system installation procedures, system performance characteristics should be verified by tests conducted under established test procedures and water analysis. Thereafter, the resulting water should be monitored periodically to verify continued performance. The application of the water treatment equipment must be controlled diligently to ensure that acceptable feed water conditions and equipment capacity are not exceeded.

4 Contaminant Nitrate (NO3-1) MCL, mg/L Treatment Methods

Nitrite (NO2-1)

10.0 (total nitrate Reverse Osmosis with Thin Film plus nitrite measured Composite Membrane (sensitive as nitrogen) to pressure) Anion Exchange (Cl- form, sensitive to sulfates) Nitrate "Selective" Anion Exchange Distillation 1.0 measured as nitrogen

The Water Quality Association publishes this Technical Application Bulletin as a service to its members and the interested public. Information contained herein is based upon the most recent public data known as of the publication date, which is printed at the bottom of the last page, and of course, cannot take into account relevant data published thereafter. The Water Quality Association makes no recommendations for the selection of a treatment system, and expressly disclaims any responsibility for the results of the use of any treatment method or device to reduce or remove a particular contaminant.

1 2

Federal Rgister, Vol. 54, No. 97, May 22, 1989. EPA Nitrate/Nitrite Health Criteria Document, 1987. 3 World Health Organization, Guidelines for Drinking Water, 1984, p. 128-134.

5 ACKNOWLEDGEMENT WQA wishes to express sincere appreciation for the unselfish contributions of the following members of WQA who contributed their time and expertise toward the completion of this bulletin. Water Sciences Committee Frank A. Brigano, Ph.D. Michael Gottlieb Joseph F. Harrison, P.E., CWS-VI Bret L. Petty, CWS-II Robert B. Ruhstorfer II, CWS-V Glen Trickle, P.E. Stephen J. VerStrat Rod Yoder

Contributors and Reviewers Jeffrey G. Franks, CWS-V Michael Gottlieb Joseph F. Harrison, P.E., CWS-VI Michael C. Keller Charles F. Michaud, CWS-VI Albert F. Preuss, Ph.D. P. Regunathan, Ph.D James Sabzali John Schlafer, CWS-VI, CI

Copyright © 2005 by Water Quality Association. All rights reserved. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electric, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. This reference document is published by:

National Headquarters & Laboratory 4151 Naperville Road · Lisle, Illinois 60532 Tel: 630 505 0160 · Fax: 630 505 9637 PRINTED IN USA 03/05


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